ADVANCED AND SUSTAINABLE MANUFACTURING METHODS OF POLYMERIC BASED MEMBRANES FOR GAS SEPARATION

Abstract

The global market outlook on the demand for gas separation technology shows a continuous
increase for the next two decades or more. Gas separation membranes represent a cutting
edge solution in the field of industrial separation processes. These specialised membranes,
designed to selectively allow certain gases to pass through while retaining others, are pivotal
in a variety of applications including carbon capture, biogas upgrade, hydrogen production,
and medical gases. Polymeric gas separation membranes have emerged as a remarkable
technology, demonstrating application potential across these industries. However, the
inherent trade-off between permeability and selectivity coupled with other challenges
associated with conventional polymeric membranes, including the non-recyclability of the
materials, solvent toxicity, as well as a fabrication technique with little or no control of the
membrane structure have hindered their widespread industrial deployment. To address most
of these identified research gaps, this doctoral research project is focused on discovering
innovative solutions, particularly in the adoption of advanced techniques and eco-friendly
materials for the fabrication of polymeric membranes. First, asymmetric membranes for gas
separation were explored, unravelling the interfacial insights and manufacturing techniques
using the hybrid of electrohydrodynamic emission (EHD) and solution casting method to
produce ZIF-67/cellulose acetate asymmetric membranes with improved gas permeability
and selectivity for CO2/N2, CO2/CH4, and O2/N2. Molecular simulations were used to reveal
the vital ZIF-67/cellulose acetate interfacial phenomena, such as higher density, chain
rigidity and others, that are necessary when engineering optimum composite membranes.
Secondly, electro-casting techniques was employed to develop cellulose acetate membranes
embedded with 1-Ethyl-3-methyl imidazolium and the structural, morphological, and gas
transport characteristics of this membranes were comparatively analysed against
conventional casting techniques. Thirdly, the recyclability of biodegradable 3D-printed gas
separation membranes was studied. Here we explored the development of a 3D printed
polyhydroxybutyrate (PHB) and recycled PHB membrane, harnessing the synergy of
advanced 3D printing technology, solvent-free fabrication processes, and the environmental
benefits of biodegradable polymers. The developed membranes were evaluated for
separation efficiency, thermal, chemical and mechanical stability, as well as environmental
impact, with emphasis on recyclability and biodegradability. The outcomes of employing
EHD and solution casting methods for membrane fabrication represent a significant
breakthrough in the field of membrane manufacturing. These techniques lead to enhanced
selectivity and performance, attributable to the improved dispersion and interaction of
particles within the membranes. Likewise, it was observed that electro-casted membranes
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exhibited a unique crystalline structure and surface topology that induced a remarkable 230%
improvement in CO2/N2 selectivity and a 110% increase in CO2/CH4 selectivity. The electric
field generated during the manufacturing process played a crucial role in altering the
supramolecular structure of the polymer, thereby reducing the tortuous diffusive path of gas
molecules, and enhancing the permeance of specific ones. The single gas permeation test of
the 3D printed membranes showed that the membranes exhibited size-selective behavior,
with permeability decreasing as the kinetic diameter of the gas increased (CO2 > O2 > CH4 >
N2). Moreover, the gas permeability values improved with the increase in PHB recycling
cycles for the three recycled PHB membranes, thus implying that membrane gas
permeability was not adversely affected by polymer recycling. Overall, this PhD thesis
showcases various innovative manufacturing realms, from advanced techniques like EHD
and electro-casting to sustainable practices involving biodegradable materials and recycling,
marking a substantial stride toward eco-friendly and efficient gas separation membrane
technology.

Date of Award	22 Jan 2025
Original language	English
Awarding Institution	University of Bath
Supervisor	Bernardo Castro Dominguez (Supervisor) & Semali Perera (Supervisor)